The present invention is directed to intelligent material handling devices that lift and lower loads as a function of operator-applied force. The devices described herein are different from manual material handling devices currently used by assembly and warehouse workers in that the devices respond to the operator's interaction with the lifting device, and not merely to an operator's pushing, depressing or squeezing of a switch or button on a control pendant.
More specifically, the present invention is directed to a class of material handling devices called balancers or lifts, which include a motorized lift pulley having a cable or line that wraps around the pulley as the pulley is rotated, and an end-effector that is attached to the end of the cable. The end-effector has components that connect to the load being lifted. The pulley's rotation winds or unwinds the line and causes the end-effector to lift or lower the load connected to it. In this class of material handling systems, an actuator generates an upward line force that exactly equals the gravity force of the object being lifted so that the tension in the line balances the object's weight. Therefore, the only force the operator must impose to maneuver the object is the object's acceleration force.
There are two ways of creating a force in the line so that it exactly equals or balances the object weight. First, when the system is pneumatically powered, the air pressure is adjusted so that the lift force equals the load weight. Second, when the system is electrically powered, the right amount of voltage is provided to an amplifier associated with the pulley drive motor to generate a lift force that equals the load weight. The fixed preset forces of balancers are not easily changed in real time, and therefore these types of systems are not suited for maneuvering of objects of various weights.
Another class of material handling device use end-effectors equipped with force sensors or motion sensors. These devices measure the human force or motion and, based on this measurement, vary the speed or force applied by the actuator (pneumatic drive or electric drive). An example of such a device is U.S. Pat. No. 4,917,360 to Yasuhiro Kojima, U.S. Pat. No. 6,622,990 to Kazerooni, and U.S. Pat. No. 6,386,513 to Kazerooni. U.S. Pat. No. 6,622,990 for a “HUMAN POWER AMPLIFIER FOR LIFTING LOAD WITH SLACK PREVENTION APPARATUS,” to Kazerooni., issued Sept. 23, 2003, is hereby incorporated by reference in its entirety. With this and with similar devices, when the human pushes upward on the end-effector the pulley turns and lifts the load; and when the human pushes downward on the end-effector, the pulley turns in the opposite direction and lowers the load.
A problem may occur when the operator presses downward on the end-effector to engage the load with a gripping mechanism such as suction cups; the controller and actuator interpret this motion as an attempt to lower the load. Also, during fast maneuvers workers can accidentally hit the loads they intend to lift or their surrounding environment (e.g. conveyor belts) with the bottom of the end-effector. In palletizing tasks, for example, workers often use the bottom of the end-effector to fine tune the location of a box or container. These occurrences may cause slack in the line since the operator might push downward on the end-effector handle to locate box, while the end-effector is constrained from moving downward. As a result, the actuator causes the pulley to release more line than necessary, thereby creating “slack” in the cable. As used herein, the term “slack” is understood to mean an excessive length of cable or line, and may or may not include instances where the line is simply not completely taut.
Once slack is produced in the line, by this or other circumstances, when the operator pushes upward on the handle, the slack line can become entangled around the operator's neck, arms or hands, or interfere with other equipment, creating the possibility for injury or damage. A slack cable is also a problem for the overall mechanics of the lift. If the lifting cable is stiff enough and slack is created in the cable, then it pushes the cable off the lift pulley that is used to wind and unwind the load cable. When tension is reintroduced into the load cable, not all of the slack comes out of the cable wrapped around the lift pulley. Repeated occurrences of slack will eventually cause the cable to come off the drum or become entangled in other components or hardware in the actuator. Covers that go over the drum are not sufficient to prevent the cable from eventually becoming entangled in the mechanics of the actuator. Slack can occur even when other end effectors are used for load gripping means. Therefore, to assure safe operation it is important to prevent slack at all times. In general, slack in the line can be dangerous for the operator and others in the same work environment.
Heretofore, a number of patents and publications have disclosed apparatus and methods for controlling slack in lift cables, the relevant portions of which may be briefly summarized as follows:
U.S. Pat. No. 6,622,990 to Kazerooni, discloses a controller for a pulley hoist arrangement, wherein the controller stops the pulley when a signal represents zero tensile force on the lift line but the end-effector is pushed downwardly by the operator. The patent is a division of allowed parent application Ser. No. 09/443,278, filed Nov. 18, 1999, now U.S. Pat. No. 6,386,513 by Homayoon Kazerooni, entitled “Human Power Amplifier For Lifting Load Including Apparatus For Preventing Slack In Lifting Cable” which parent application claims the benefit of U.S. Provisional Application Nos. 60/134,002, filed on May 13, 1999, Application No. 60/146,538, filed on Jul. 30, 1999, and Application No. 60/146,541, filed on Jul. 30, 1999. Both the parent and provisional applications are also hereby incorporated by reference in their entirety for their teachings.
U.S. Pat. No. 5,960,849 to Delaney et al., issued Oct. 5, 1999, teaches an apparatus for detecting the occurrence of slack in a cable as well as compensation for cable slack in a door operator.
U.S. Pat. No. 2,636,953 to Hunt, issued April 28, 1953, discloses an electric safety switch for a load carrying device, to automatically stop downward motion when cable tension falls below a predetermined minimum.
As briefly described above, during the operation of an intelligent lift, such as the G-force lift manufactured and sold by Gorbel, Inc., an operator may move the control handle in such a way as to place the lift, and its associated load, into a condition where the lift cable experiences some slack between the actuator and the handle/load. While the G-force Lift is programmed to reduce the likelihood of such a situation (see e.g., U.S. Pat. No. 6,622,990, previously incorporated by reference), one aspect of the present invention is directed at the failsafe detection of cable slack. Another aspect of the invention is directed at monitoring of the number of winds of cable left on the lift pulley of the actuator, so as to assure that, at a minimum, approximately two winds (revolutions) of line or cable are wrapped about the lift pulley. In combination, these aspects are safety features directed at preventing the unwind of the cable from a lift pulley, thereby preventing the possible jerking of a load, the potential malfunction of the lift, and the various safety concerns set forth above.
In accordance with the present invention, there is provided a human power amplifier assist device, including: a lift pulley with a cable wound thereon; an actuator arranged to turn the lift pulley so as to wind and unwind the cable; an end-effector connected to the cable and connectable to a load, the end-effector including a sensor for detecting an operator-applied force on the end effector; a controller for controlling operation of the actuator, the controller being responsive to a first signal from the sensor representing operator-applied force and at least one additional signal representing the condition of the cable; and the controller being programmed to cause the actuator to wind and unwind the cable in response to the first signal, and to override the control as a function of the first signal in response to the additional signal.
In accordance with another aspect of the present invention, there is provided a device for monitoring the condition of a cable wound on a lift pulley, and generating at least one signal indicative of the condition, including: a cable slack sensor; and a cable end sensor; wherein the at least one signal representing the condition of the cable includes a cable slack signal generated by the cable slack sensor and a cable end signal generated by the cable end sensor.
In accordance with yet another aspect of the present invention, there is provided a method for monitoring the condition of a cable wound on a lift pulley, including: monitoring the slack condition of a cable with a slack sensor; and monitoring the length of cable, with a cable end sensor, to determine when a predetermined maximum length of cable has been unwound.
One aspect of the invention is based on the discovery that further failsafe manual sensors may be employed to assure that abnormal use or abuse situations do no result in a slack cable condition on a lift device. This discovery avoids problems that arise in lift systems, including intelligent lifts, whereby sensing of the operator's applied force may result a slack cable condition.
This aspect is further based on the discovery of techniques that can be used during normal operation of such lifts, whereby conventional mechanical sensors or switches may be employed to detect and minimize or prevent slack cable conditions. This aspect of the invention can be implemented, for example, by separate or a combination of sensors for the detection of cable slack and tracking of cable winding on a lift pulley.
The technique described herein is advantageous because it is simple and can be adapted to any of a number of lift devices employing a cable and lift pulley on which the lift cable or line is wound. In addition, it can be used to in the automated control and customized setup of a lift to facilitate improved performance. As a result of the invention, the performance and safety of intelligent lifting devices is improved. One of the most important properties of the invention is that the actuator and pulley operate under the control of the operator on the end-effector so as to follow the operator's hand motion upwardly and downwardly—yet the line does not become slack if the end-effector is physically constrained from moving downwardly while the end-effector is pushed downwardly by the operator.
The present invention will be described in connection with a preferred embodiment, however, it will be understood that there is no intent to limit the invention to the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.